1. Field of the Invention
The invention relates to an apparatus for the generation of primary electrons from a cathode for maintaining forced gas discharges and, more particularly, to a hybrid cathode for a duoplasmatron ion source.
2. Description of the Prior Art
Cathodes with filament-type emitters are known in the prior art (M. V. Ardenne, "Tabellen zur Angewandten Physik" Vol. 1, 2 edition, page 653, Berlin 1962). They have, however, a relatively short life span since the filament is rapidly worn by ion bombardment (cathode sputtering). As a result, the heating current has to be frequently adjusted to the reduced cross-section of the cathode filament if the filament becomes too weak as a result of overheating, shortenings of the filament windings may occur which would lead to an immediate destruction of the cathode. Also, the power supply feed throughs or penetrations usually used with such cathodes include ceramic materials which are very sensitive to temperature differentials particularly when subjected to the weight of the power supply cables. It is also difficult to keep them clear from metals condensing thereon so that short circuits may occur.